This invention relates to coiled electrode assemblies having conductive tabs, methods of attaching the conductive tabs to the coiled electrode, and electrochemical cells employing such assemblies.
Electrochemical cells employing coiled electrode assemblies are widely known in the art. In many of these cell structures the coiled electrode assembly is inserted into a composite housing which serves as the current conductive terminals for the cell. When this type of cell is assembled, a conductive tab must first be secured to the electrodes by an appropriate means such as welding.
Cells employing coiled electrode assemblies can be produced using various electrochemical systems such as nickel metal hydride, nickel cadmium, nickel zinc and the like. When using nickel metal hydride cells, the negative electrode of nickel metal hydride cells is typically a hydrogen storage electrode in the form of a metal hydride. The positive electrode is typically nickel hydroxide. These cells also contain a separator and electrolyte, as is known in the art.
The positive electrode strip is generally the outermost wound electrode for nickel metal hydride cells and has a conductive tab secured to a selected area of the carrier at one end and to the cell housing at the opposite end. Prior to securing the conductive tab to the electrode, a selected area of the conductive carrier must be cleared of any active electrode material. Conventionally, this removal is by processes such as air blasting, scraping, suction, ultrasonic clearing and the like. However, use of these methods is carrier (substrate) dependent both for efficiency of removal of active material from the substrate and strength of the resulting weld connection of the conductive tab to the substrate.
With the development of conductive carriers made of felt, foam and other fragile substrates, the task of removing active material from the substrate and attaching a conductive tab has become more difficult. Various methods have been used to break or loosen the active material from the substrate, such as ultrasonic removal of active material from the desired area, removal of active material from the substrate along an entire edge of the electrode, attaching conductive tabs in the shape of a "t" or "v" or "h" in order to strengthen the tab area, and others.
Although removal of active material from the entire length of the electrode contributes to manufacturing efficiency of these type cells, the trend today is to maximize capacity by reacting as much of the active material present in the electrochemical cell as possible. The need still exists for methods of manufacturing coiled electrode assemblies which substantially remove only a small section of active material from fragile substrates without weakening or damaging the substrates, and which allow for attachment of a conductive tab to the thus cleared substrates.